It looks overfiltered I think, your losing all the details. It's fine to use filters, but try duplicating the original
scan layer and filter the duplicated layer, then turn down the opacity, or use 'soft light' for the duplicated and
filtered layer.

How big is the original scan? And does it look grainy before you coverted to JPEG? Because I think the 'grainy-ness' you
mentioned may be due to JPEG compression. JPEGs and reds/oranges never get along nicely, so when you save as from a PSD
file, you'd have to use the JPEG optimizer and set the compression value to the lowest possible.

But like gaara said, try using http://imageshack.us to post the
original size wallpaper so we can see it better. :)

Much okay with the the text, without the dropshadow. But when comparing those two, it's like you change the whole
wallpaper. I noticed the background also changed , like you duplicated the whole wallpaper, and applied the soft light
effect. Hmm...